i can't defrag or scan-disk

each time i run my scandisk it rins for about 5 mins ,then comes up with a massage saying that scandisk has started 10 time,you may need to shut some programs down,(i use a" end it all" program)so i cant understand that .whan i run my defrag it never seems to finish it can run for a day and in the end the screen just frezes ?(running on win 98 )